Group Reseach Interests
The intersection of metallurgy, solid mechanics and chemistry is currently at the forefront of several important engineering challenges including: prognosis of environmentally degraded airframe and ship components, design of the maintenance protocol for storage and distribution of metal embrittling H2 for the hydrogen energy economy, material embrittlement and fatigue issues in the resurgent nuclear power field, and alloy selection and life prediction for bio-medical engineering.
Proper modeling and prediction of the fatigue or fracture behavior of complex metal components necessitates an understanding of the pertinent microstructure and damage physics; specifically the interaction of the mechanical driving force, chemical driving force, and the material response. Such understanding is also critical for alloy development. As such our research focuses on the interaction of localized stress/strain with environment conditions, with a particular emphasis on behavior at the crack tip. In general, experimental data from controlled environmental testing are coupled with high fidelity characterization techniques to gain mechanistic understanding of the damage process; such knowledge is used to inform theoretical and engineering level models.
Current research is centered on aluminum alloys, ultra-high strength stainless steels and nickel-based super-alloys. The effect of water vapor pressures and temperatures typical of airframe operation are being investigated to quantify and better understand the material properties of legacy and next generation aerospace Al; as necessary to maintain structural integrity and safely extend the useful life of airframes. The effect of corrosion damage is also being investigated; mechanistic studies are being used to inform engineering level prognosis techniques. Additionally, the effect of chloride environments (typical of sea-coast or marine environments) on the fatigue behavior of ultra-high strength stainless steels is being investigated. The use of such steels will enable a reduction in the use of coatings that are both hazardous to personnel and deleterious to the environment. Additionally, stress corrosion cracking of 5xxx-series Al alloys and Ni-based super-alloys aims to understand the mechanistic causes of the high dependence on cathodic polarization and use this knowledge to inform alloy development, preventive actions, and corrective maintenance. Collaboration with industry partners has enabled the development of a novel and unique coupling of a testing method and software package that will enable estimates of the safe operating life for components subject to these aggressive environments.
Fatigue and Fracture
A major research focus of this lab group is the environmental fatigue failure of various high strength stainless steels and aerospace aluminum alloys. Environmental factors, such as salt and pH, are known to be particularly deleterious to the safe functional life of materials engineered for field use. Better understanding of environmentally enhanced fatigue will enable better design and prognosis in field evaluations of engineering components.
Research in this field tends to focus on how different environmental factors affect fatigue crack growth kinetics and crack tip progagation mechanisms. Crack tip propagation and crack growth kinetics are a topic of heavy research in the Burns Group as these phenomena play a large role in the endurance limit of a field-use material. The environment at a crack tip may also differ from that of the bulk, potentially creating further complexity in modeling.
Stress Corrosion Cracking
Stress Corrosion Cracking (SCC) is also an important research interest in the Burns lab. Currently, researchers are studying how SCC manifests in different materials (nickel superalloys, aerospace aluminum alloys) under different loading conditions and environments. Hydrogen environment assisted cracking (HEAC) is a common SCC mechanism and is therefore a significant area of research. Characterization of SCC requires high fidelity crack growth measurement, achieved through cutting-edge direct current potential drop (dcPD) crack monitoring systems. The crack growth kinetics are coupled with fractographic and metallurgical analyses to inform modeling and component lifetime predictions during SCC.